My fvScehemes and fvSolutions are attached. I slightly changed them from the ones you can get from the propeller tutorial as I would like to use a k-omega model. Don't know if in doing so I messed them up…

Any help would be greatly appreciated.

linnemann

April 16, 2012 05:26

Hi

I would suggest doing the following until it stops blowing up.

Change to upwind on U.

And relax the components by 0.5.

If it stops blowing up you can then try to switch to higher order schemes and decrease the relaxation.

lovecraft22

April 16, 2012 05:32

Thank you Linnemann.

Relax the components by 0.5 means that I need this in my fvSolutions:

Code:

relaxationFactors
{
"(U|k|epsilon).*" 1;
}

correct?

About the rest, what do you mean with change to upwind on U and switch to hig order schemes?

Thank you again for your help!

linnemann

April 16, 2012 05:58

yes

relaxationFactors
{
"(p|U|k|epsilon).*" 0.5;
}

in fvSolutions

and

div(phi,U) Gauss upwind;//

in fvSchemes

you are using linearUpwind which is a higher order scheme and thus inherently more unstable.

lovecraft22

April 16, 2012 08:42

Thank you linnemann, unfortunately had no luck with your tips…
First of all I increased the time step from 1e-5 to 1e-4 and my simulation blew up at time 0.0266.
So I changed this line I had in my fvSolution:

Code:

"(U|k|epsilon).*" 1;

to this:

Code:

"(p|U|k|omega).*" 1;

as I'm using the k-omega model and the simulation blew up again at 0.0266.
So I changed the line to this:

For more about these algorithms, you'll have to read up on CFD literature ;)

Best regards,
Bruno

calim_cfd

April 17, 2012 15:49

just a thought... you know your running an incompressible solver and your using a reference pressure of 1atm

Code:

pRefPoint (0.1 0.1 -0.005);
pRefValue 1e5;

have you handled all the other variables to adjust to this value? :eek:

linnemann

April 17, 2012 15:58

Hi lovecraft

Had a look at your case and it looks like you haven't (not to be rude) understood the setup involving rotating stuff.

If you follow the tutorial

/tutorials/incompressible/pimpleDyMFoam/mixerVesselAMI2D

I think you will get a better understanding of the whole setup involving rotating parts.

Back to your case.

I had to split it up into two meshes and then merge them back together and attach them using AMI's. You cant have a moving mesh where you only have one mesh and a zone. If you want to do it this way you should use the steady MRF approach.

Also a lot of your BC's where wrong for such a case.
Here is a nice little animation of it running.

And to follow up on the difference transientSimpleDyMFoam has some hard-coded stuff that makes it more stable, but it should be able to tweak pimpleDyMFoam to have a similar stability.

lovecraft22

April 17, 2012 17:10

Thank you a lot linnemann, that's really great! I'll have a look at the setup tomorrow. Could you also explain me what commands you ran?

Thanks again!

lovecraft22

April 17, 2012 18:07

I did some digging around and also looking at the case you uploaded I think I understood this:

1. You need to create an interface between the rotating and the stationary meshes. In my case it was a cylinder. This is the AMI (Arbitrary - btw, why "arbitrary??" - Mesh Interface);
2. You need to mesh the two regions separately, making sure you have the same cell dimensions on the AMI;
3. Merge the two meshes using mergeMesh on the running case and then run it.

I'll dig deeply on the propeller tutorial tomorrow.
What I did wrong (and I'm sorry for having posted here and on another discussion my wrong conclusions about that…) was that I only set the rotating region as a zone. This is what I usually do for the MRF and, at this point, I hope that at least is correct…

Looking forward to try an run it as I'm getting really excited about that!

Hello linnemann, appreciate your effort on pimpleDyFoam above.
plz find my case folder with implementation of rotating cube.
* I have only done the meshing of rotor stator inside rocube/Mesh folder.
* the next step would be to merge rotor-Mesh and stator-Mesh!!!

How to go about it?

Note: Still the case is not fully modeled, so most of the BC files are missing.